The present invention generally relates to semiconductor photodetectors, and more particularly to an integrated circuit device that includes a photodetector and a process for its fabrication.
Semiconductor photodetectors are well known in the art. U.S. Pat. Nos. 4,670,765 and 5,177,581 disclose examples. Often such photodetectors are integrated with other circuit elements on the same semiconductor chip. U.S. Pat. Nos. 5,049,733 and 5,105,090 disclose examples. Another example that is compatible with a more advanced fabrication process is disclosed in U.S. Pat. No. 5,994,162. These five patents are incorporated by reference herein as background technology.
Semiconductor manufacturers have developed complex process technologies that permit fabrication of high circuit densities on a single silicon chip. Many such technologies have the flexibility of forming either bipolar transistors or field-effect transistors (FETs), or more typically, both types of transistors on the same chip. When both complementary forms of metaloxide-semiconductor FETs (both N-channel and P-channel MOSFETs) are formed with bipolar transistors on the same chip, the generic process technology is referred to as BiCMOS. Advanced BiCMOS processes provide IC devices that operate at high frequencies suitable for high performance electronic products. The incorporation of a photodetector onto a single semiconductor chip may involve modification of an existing process technology that is compatible with the end-use application. It would be desirable, therefore, to facilitate such a process modification in a way that does not significantly change the structures and functions of basic circuit elements (transistors and capacitors), while minimizing any increase in the number and complexity of process operations.
In accordance with a principal object of the invention, a photodetector is integrated with high speed bipolar transistors and other semiconductor elements on a single chip, using advanced BiCMOS process technology. The photodetector comprises a thin, light-transmissive layer disposed above a diode having a PN junction lying generally parallel to the light-transmissive layer. The diode is physically isolated from other circuit elements on the same chip, and is electrically interconnected with the chip circuitry using conductive interconnects. The material that forms the light-transmissive layer extends laterally over regions of the chip that include these other circuit elements, which primarily include different types of bipolar transistors. The fabrication process accommodates inclusion of the photodetector structure with a minimum of photolithographic operations by incorporating the laterally extending portions of the light-transmissive layer into the structures of various transistors on the chip without degrading their characteristics.